Henry Lewis Benning was born in Columbia County on April 2, 1814, to Malinda Meriwether White and Pleasant Moon Benning. His family moved to Harris County in 1832, while Benning was studying at the University of Georgia in Athens. He graduated in 1834 and then studied law in Talbot County with George W. Towns. In 1835 he was admitted to the bar in Columbus, which was thereafter his permanent home. From 1837 to 1839 he served as solicitor-general in Columbus, and in 1839 he married Mary Howard Jones (a first cousin to the Georgia writer Augusta Jane Evans), with whom he had ten children.

Benning practiced law privately before running unsuccessfully in 1840 for a seat in the Georgia General Assembly. But he did not lose his interest in politics, and in 1850, during the sectional crisis, he was one of Georgia's delegates to a convention of nine slaveholding states, held in Nashville, Tennessee, to determine the Southern course of action if slavery were banned in the western territories. While the resolutions of the convention helped lead to the Compromise of 1850, which temporarily averted secession, Benning introduced resolutions in Nashville that strongly defended slavery and supported a state's right to secede.

Returning to Georgia, Benning again tried for political office, this time running for the U.S. Congress on a Southern Rights platform, but he was again defeated. Turning back to his roots in the law, he was elected associate justice of the Georgia Supreme Court in 1853 and served on the court for six years. In the case of Padelford v. Savannah (1854), Benning made the claim that state supreme courts were coequal with the U.S. Supreme Court on the matter of constitutional issues. This powerful argument for states' rights garnered Benning much support in the South.

Benning was chosen as chairman of the Georgia delegation to the Democratic National Convention of 1860. Led by Benning, the Georgia delegation and most Southern delegates walked out of the convention when the national party refused to put a plank supporting slavery into its platform. The split in the Democratic Party virtually assured the election of the Republican candidate, Abraham Lincoln. Lincoln was opposed to the expansion of slavery into the West but insisted that he would not and could not interfere with the institution where it currently existed. Many Southerners did not believe him.

In the wake of Lincoln's election, Benning became one of Georgia's most vocal proponents of secession. On November 19, 1860, he delivered a speech before the state legislature urging immediate secession, ending the speech by saying,"[L]et us do our duty; and what is our duty? I say, men of Georgia, let us lift up our voices and shout, 'Ho! for independence!' Let us follow the example of our ancestors, and prove ourselves worthy sons of worthy sires!" Benning did more than just speak; he briefly presided over Georgia's secession convention (until the election of George W. Crawford as convention chair) and helped to draft the state's Ordinance of Secession. After Georgia seceded from the Union in January 1861, Benning was dispatched as Georgia's representative to Virginia, which was still debating the secession question. There, he gave a speech before the Virginia secession convention, arguing that separation from the Union was the only way to preserve slavery.

With the outbreak of the Civil War, Benning helped to raise the troops that became the Seventeenth Georgia Infantry, and he was chosen as colonel in August 1861. Most of his military service was in Virginia. He fought in the Seven Days' Battles in the summer of 1862 and at Second Manassas, where he earned the nickname "Old Rock" for his steadfastness in battle. At the Battle of Antietam, in Maryland, his troops played a pivotal role in holding a bridge against overwhelming odds, allowing time for Confederate reinforcements to arrive and prevent a rout of the Confederate army. By January 1863 Benning had risen to the rank of brigadier general. On July 2, 1863, he led his men on an unsuccessful assault of Little Round Top at Gettysburg, Pennsylvania.

Benning and his troops were part of the contingent sent west in the fall of 1863 to reinforce Confederate forces trying to prevent a Union invasion of Georgia. He participated in the Confederate victory at the Battle of Chickamauga in September 1863, helping to lead the charge that broke the Union lines and having two horses shot from under him. He also was instrumental in the campaign at Knoxville, Tennessee, later that year. By the spring of 1864 he was back in Virginia, where he was wounded in May at the Battle of the Wilderness. After recovering he again assumed command of his troops in Petersburg, Virginia, in November 1864, and he was with them in April 1865 at the final Confederate surrender in Appomattox, Virginia.

After the war, Benning, like so many other southern planters, returned home to a devastating economic situation. Much of his wealth had been invested in slaves and land, but the slaves were now gone, and much of his land was ruined. Benning returned to the practice of law and began rebuilding his finances; his wife died in 1867. Benning continued to practice law right up until his death; in fact, he was on his way to a court appearance when he suffered a major stroke and died on July 10, 1875. He was buried in Linwood Cemetery in Columbus.

In 1918 the U.S. Army established its infantry school at a camp located partly in Muscogee County and partly in Chattahoochee County. At the request of the Columbus Rotary Club, the camp (and later fort) was named for Benning.